Chitosan-fabricated Ag nanoparticles and larvivorous fishes: a novel route to control the coastal malaria vector Anopheles sundaicus?

Mosquitoes represent a key threat for millions of humans worldwide, since they act as vectors for malaria, dengue fever, yellow fever, Zika virus, filariasis, and encephalitis. In this study, we tested chitosan-synthesized silver nanoparticles (Ch–AgNP) using male crab shells as a source of chitosan, which acted as a reducing and capping agent. Ch–AgNP were characterized by UV–Vis spectroscopy, FTIR, SEM, EDX, and XRD. Chitosan and Ch–AgNP were tested against larvae and pupae of the malaria vector Anopheles sundaicus under laboratory and field conditions. Antibacterial properties of Ch–AgNP were tested on Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, and Proteus vulgaris using the agar disk diffusion assay. The standard predation efficiency of the mosquito natural enemy Carassius auratus in laboratory conditions was 60.80 (on larva II) and 19.68 individuals (on larva III) per day, while post-treatment with sub-lethal doses of Ch–AgNP, the predation efficiency was boosted to 72.00 (on larva II) and 25.80 individuals (on larva III). Overall, Ch–AgNP fabricated using chitosan extracted from the male crab shells of the hydrothermal vent species Xenograpsus testudinatus may offer a novel and safer control strategy against A. sundaicus mosquito vectors, as well as against Gram-negative and Gram-positive pathogenic bacteria.